This is a delicious and unusual marmalade with a gorgeous color. I originally found a version of this recipe by doing a search for "blood oranges" when they were in season. I have since tweaked the recipe, and this is my own variation.
Put very thinly sliced blood oranges and lemon into a non-reactive pan with the water over low heat. Cook for 1 hour, stirring occasionally. Turn off heat and let sit, covered, overnight.
Sterilize the jars in boiling water for 15min. Do not boil the canning lids, but scald them in the just-boiled water after the heat is turned off. Leave the jars and lids in the water until needed.
Meanwhile, measure the citrus pulp, rind and liquid. For every cup of citrus mixture, add 3/4 cup of sugar.
Return the citrus and the sugar to the pot over medium high heat and add the rosemary. Bring to low boil, stirring often. Reduce the heat and cook at a low simmer for 20 minutes, stirring occasionally.
Turn off the heat. Test for gel by putting a small spoonful of the marmalade on a plate in the freezer for one minute. The marmalade should form a skin and wrinkle when pushed (you can back this up with the spoon “sheeting” test if you are familiar with it). If not ready, return to the heat and test again a few minutes later. When the gel stage has been reached, turn off the heat, remove the rosemary, and ladle the marmalade into clean sterilized jars.
Process in a boiling water bath (water at a full rolling boil covering the jars by at least one inch) for five minutes.